1) The 9A34 is twice the size of the ETX30L (and twice the cost). I will freely admit that I probably would choose something larger if I had to deal with, say, Michigan or upstate NY winters. That said, it has been fantastic in the DC winter, even when left outside.

2) Downsides are: Running the stereo with the engine off is asking for trouble. This goes for ANY smaller battery. I've never tried to experiment with how long I can get away with this for, but it's not something that I would recommend. And if anything, these batteries are better in a DD because sitting for lengthy periods of time will allow them to get drained by the car.

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